1. Field of the Invention
The present application relates to an illumination apparatus, and more particular to an illumination apparatus with high heat conductivity and insulative capability.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The light emitting diodes (LEDs) have been used since 1960s, and usually used as indicating or signal lights. Because traditional LEDs do not have high power consumption, heat dissipation of LED packaging was not an issue. In recent years, lightness and power consumption of the LEDs used for television backlights or illumination have become increasingly high, and therefore heat dissipation becomes a crucial problem for LED illumination applications.
A traditional incandescent lamp dissipates about 70% heat by infrared radiation, so that heat accumulation in the lamp is not obvious. However, an LED usually emits visible light or ultra-violent light, and therefore it does not easily dissipate heat by radiation. In addition, small LED packaging area is hard to dissipate heat efficiently, resulting in LED luminous decay. Therefore, heat management is important for LED illumination applications.
Traditionally, LEDs transfer heat to a substrate through a metal lead frame, and thermal resistance of package is very high, e.g., 250-300° C./W. Then, LEDs are surface-mounted on to circuit board for packaging, in which a resin layer (FR4) adhered to the circuit board is used for heat transfer. The large heat dissipation area can significantly decrease thermal resistance. However, FR4 may not be suitable for packaging of high power LED due to its low heat conductivity coefficient though it is still used in low-end products owing to its low cost. To increase heat conductivity, ceramic substrates are used; however, the ceramic substrates are brittle and costly. In addition, a metal core circuit board (MCPCB) using an aluminum substrate may be used. MCPCB has good heat conductivity, but it cannot provide good insulation. Therefore, MCPCB needs to associate with extra insulative design.
Nowadays, as to LEDs, heat-source devices or other electronic devices, a thermal interface material is employed to combine such devices with a heat dissipation structure. The thermal interface material usually contains an organic silicon polymer, organic phase transition material or heat-conductive paste. Although these materials perform good heat conductivity, they are not sticky enough. Therefore, the combination needs auxiliary components such as screws, rivets, or tenons. These traditional materials may degrade to generate small molecules cracking products after being used for a long time, resulting in lower heat conductivity and contamination to electronic devices.
It is necessary to take both the painting and process behaviors into account for commercial heat conductive pastes and double-side adhesives of epoxy resin series. Large amount of ceramic powder increases heat conductivity; however, excessive ceramic powder causes high viscosity which is detrimental to painting process and tremendously reduces adhesive strength.
Accordingly, it is demanded to provide an effective solution for LED illumination in consideration of insulation, heat-conductivity and adhesive strength in the situation without auxiliary fixing components such as screws.